For many decades, television signals have been transmitted to television subscribers terrestrially and via cable. In Europe, for example, the PAL standard is used for this purpose, and in North America the NTSC standard. Since all television sets in the respective countries are suitable for receiving the television signal encoded e.g. according to the PAL standard, only one television signal needs to be transmitted for a television program. As a result, a transmission of a plurality of differently encoded television signals of a television program, for example as a function of an image size or a performance capability of the television sets, is not required.
Due to the current introduction of new terminal devices, for example mobile terminals with small screens, it will no longer be possible in the future to provide a single television signal of a television program for all terminal devices. Furthermore it may also be desired to provide different television subscribers with television signals of different quality. In this case, for example, a low-quality television signal, in monochrome for example, is provided for a television subscriber who pays a low monthly fee, whereas for a higher fee a high-resolution color television signal is supplied.
New types of data compression algorithms, such as a video coding standard ITU-T H.264 for example, as well as metadata languages, such as e.g. XML (XML=Extended Markup Language), were developed in order to satisfy these requirements. With the aid of said metadata languages, contents of a document and/or a data stream, such as of a television or video signal for example, can be described in a structured manner by means of an XML schema language definition. Based on this definition, information can be obtained as required, with the aid of which information a scaling of the television or video signal for different television subscribers can be realized.
From the prior art, it is known to use XML-based descriptions of data streams in which individual components of the data stream are described or marked according to their syntactical meaning by means of BSD units (BSD=Bitstream Syntax Description) with freely addressable gBSD units (gBSD=generic Bitstream Description) with regard to different adaptation possibilities. A detailed description can be found in document [1] listed at the end of this application. These descriptions of the data stream are used in order to adapt the data stream to the requirement, for example in terms of data rate or quality of a television signal, of an end subscriber, such as e.g. a television subscriber. For this purpose the description of the data stream can first be suitably transformed, with the data stream then being adapted based on the transformed description.
A Bitstream Binding Language (BBL) method, by which a synchronization can be performed, is known from document [4]. Since BBL is based on XPath during the fragmentation of metadata and a description of a section of the metadata using XPath accounts for a sizable quantity of data, a large overhead is generated by this method. A proprietary method is proposed for the fragmentation of the media data, as a result of which it is generally not made possible to synchronize different data types.
Requirements for streamable digital items are presented in document [2]. These requirements are based on the gBSD description, a distributed and dynamic adaptation being proposed for metadata.
Document [3] discloses two methods in which an adaptation of data streams for streaming applications can be performed with the aid of the gBSD description and XSLT description.